The present invention relates generally to a method and an apparatus for reproducing a recorded video signal. More particularly, the invention relates to recorded video signal reproduction applicable to digital video tape recorders.
Some recent digital video tape recorders have systems for recording and distributing samples from each field of image data among a plurality of separate track blocks on a single track, such as by shuffling or interleaving for added data fidelity.
The organization of data recorded on the digital video tape is shown diagrammatically in FIG. 2. FIG. 2A shows one synchronization block containing image data (DATA) for one-fourth horizontal line (1/4H). In addition to the DATA block, the synchronization block (SYCB) includes synchronization code (SYNC CODE), address code and cyclic redundancy check code (CRC CODE) blocks. A number of synchronization blocks (SYCB) are strung together to form a track block (TRK) covering 1/N field, as shown in FIG. 2B. N, i.e. 10, track blocks (TRK) form one field block (FIB), as shown in FIG. 2C. This one field block (FIB) contains image data covering one field. In the reproduction process, the image data recorded in each ten track blocks is reproduced by means of a reproducing head and recorded in a field memory. The image data for one field is then retrieved from the field memory at a predetermined speed for reproduction on a video monitor.
Two field blocks (FIB) form one frame block (FLB). The frame block (FLB) thus contains image data for successive odd- and even-numbered fields including image data for one screen page on the video monitor.
The image data organized as above is recorded on the video tape in the form shown in FIG. 3. Four recording/reproducing heads 2A, 2A' and 2B, 2B' are used to record the image data on the video tape. During recording, the video tape is driven at a predetermined constant speed. The recording/reproducing heads 2A, 2A' and 2B and 2B' are mounted on a rotary drum 3 for rotation therewith in synchronism with the video tape drive. Each pair of recording/reproducing heads 2A, 2A' and 2B, 2B' are arranged side-by-side and the two pairs are diametrically opposed. Each pair of heads 2A, 2A' and 2B, 2B' serves to record data for two neighboring track blocks simultaneously. First (odd number) record fields RE.sub.1 consisting of ten track blocks each and second (even number) record field RE.sub.2 also consisting of ten track blocks are recorded alternatingly.
The image data recorded on the video tape can be reproduced in various ways. For example, the recorded image data may be reproduced in a normal REPLAY mode in which the video tape 1 is driven at the predetermined normal speed, a HIGH-SPEED SEARCH mode in which the video tape is driven at a much higher speed, for example at a speed 8-times faster than the normal speed, a SLOW mode in which the video tape is driven a slower speed, e.g. 1/3 the normal speed, and a STILL mode in which the tape drive is temporarily stopped.
In the normal REPLAY mode, the recording/reproducing heads 2A, 2A' and 2B, 2B' can scan every track block in order to pick up all of the image data at relatively high fidelity. On the other hand, when the video tape recorder is operated in SLOW mode, the heads 2A, 2A' and 2B, 2B' scan across the tape as shown in broken line in FIG. 3. As shown in FIG. 3, the scanning angle of the heads is steeper than the angle of the track blocks, so that the heads tend to scan more than one track block in each scan cycle. Therefore, the reproduced input video signal Vin contains image data for more than one track block.
This will not cause serious problems as long as the heads scan track blocks within the same field (also called "record area"). However, when the heads cross track blocks from different, adjoining record areas, image data from both record areas will be included in the input video signal Vin. For example, when heads scan the first track block A of the first record area RE.sub.1, they tend to also scan the last, i.e. tenth track block J of the preceding second record block RE.sub.2. In this case, the input video data contains image data from both the first and second record areas RE.sub.1 and RE.sub.2. This means that the input video signal Vin includes both odd-numbered field image data and even-numbered field image data. This requires special signal processing to separate the odd-numbered field image data from the even-numbered field image data.
In particular, when the tape drive is switched between forward drive and reverse drive, proper time sequence control is needed for image data picked up before and after reversing the tape drive direction, so that the video image displayed on the video monitor will not be disrupted or distorted.
In order to ensure good video fidelity when reversing the tape drive direction, it is necessary to temporarily hold the system in the STILL mode for a given period during which a single constant image will appear on the video monitor.